This section provides background information related to the present disclosure which is not necessarily prior art.
Hydraulically operated clutches generally include a piston which applies force to the clutch system to engage the clutch plates. In order to have low parasitic drag when the clutch is open, there needs to be clearance between the plates, which rotate relative to one another. Since there are often many plates in a clutch, this means that the overall axial space in a clutch can be substantial. Thus, for the clutch plates to reach maximum separation for low drag torque, the piston must retract a considerable distance from the point of engagement. Typically, for the piston to move from the fully retracted position to engage the clutch plates, the piston must first take up all of this distance before the clutch will start transmitting a usable amount of torque. In order for the piston to take up this distance quickly, a high flow of hydraulic fluid to the piston is required during the initial actuation. As the clutch plates are not engaged during this initial movement of the piston, the fluid can be provided at a lower pressure. Once the clutch plates begin to engage, the piston has less distance to travel before the clutch is fully engaged, thus the high flow rate is no longer needed. Instead, a higher pressure is required to force the clutch plates into complete engagement. These two requirements are diametrically opposed to each other when designing a hydraulic actuation system. The present invention pertains to an actuator of such a hydraulic system that is capable of both rapid take-up and high pressures.